Study of defects evolution in GaN layers grown by metal-organic chemical vapor deposition

GaN layers were grown on c-plane sapphire substrates by metal-organic chemical vapor deposition with a conventional two step growth method. The effect of the three-dimensional (3D) growth mode time (t(3D)), which depends on trimethylgallium flow rate and growth temperature, on the crystalline quality of the GaN layers was investigated by high resolution x-ray diffraction. Tilt and twist angles were estimated from full width at half maximum (FWHM) of the omega rocking curves (omega-RCs) recorded from the planes parallel and perpendicular to the sample surface. Grazing incidence x-ray diffraction was used for a direct measurement of the twist angle. The threading dislocation densities of GaN layers were estimated from the FWHM values of (0002) and (10 (1) over bar0) omega-RCs. It was found that while the screw-type dislocations were independent of t(3D), the edge-type dislocation density decreased with increasing t(3D). Investigations of the structural defects using transmission electron microscopy showed that almost all dislocations generated during the growth of GaN were pure edge or mixed type. (c) 2008 American Institute of Physics.